Cathode active material and method for preparing the same

Abstract

A positive electrode active material and a method for preparing the same, wherein the positive electrode active material includes secondary particles made up of primary particles, and the primary particles are Li 1+a Fe 1-x-y Mn x A y The cathode active material contains (PO4), and satisfies -0.1 ≤ a ≤ 0.4, 0.5 ≤ x ≤ 0.7, and 0 ≤ y ≤ 0.01, where A contains at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and the crystallinity of the cathode active material is 98% or higher. Because the cathode active material has high crystallinity, its ionic conductivity and electronic conductivity are high, and when applied to a lithium-ion battery, the battery's magnification performance can be greatly improved.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion batteries, relates to a positive electrode active material, and particularly relates to a positive electrode active material and a preparation method thereof.

Background Art

[0002] Lithium-ion batteries are widely applied in fields such as transportation power sources, power storage power sources, mobile communication power sources, new energy storage power sources, and aerospace military power sources due to their high energy density, high safety, no environmental pollution, small size, and light weight. With the continuous development of lithium-ion batteries, the market is demanding higher capacities and cycle lives for lithium-ion batteries.

[0003] As an important component of lithium-ion batteries, the positive electrode active material occupies a large proportion in lithium-ion batteries, so the performance of the positive electrode active material greatly affects the performance of the battery. Currently, the types of positive electrode active materials mainly include LiCoO2 positive electrode materials, LiNiO2 positive electrode materials, Li-Mn-O-based positive electrode materials, LiFePO4 positive electrode materials, conductive polymer positive electrode materials, etc. Lithium iron phosphate positive electrode materials have attracted the attention of the industry due to their advantages such as high theoretical capacity, low price, environmental friendliness, stable structure, and long cycle life, but their discharge voltage and energy density are still not ideal. Lithium manganese iron phosphate, as a solid solution compounded with lithium manganese phosphate and lithium iron phosphate, has improved both energy density and discharge voltage, but its ionic conductivity and electron conductivity are low, resulting in poor rate performance of the battery.

[0004] Therefore, it is necessary to urgently develop a high-conductivity lithium manganese iron phosphate positive electrode active material to improve the rate performance of the battery.

Summary of the Invention

Problems to be Solved by the Invention

[0005] To address the above-mentioned defects, this invention provides a positive electrode active material that has high ionic conductivity and electronic conductivity, and can significantly improve the magnification performance of lithium-ion batteries.

[0006] This application provides a method for preparing a positive electrode active material, the positive electrode active material prepared by this method having high ionic conductivity and electronic conductivity.

[0007] This application provides a positive electrode sheet comprising the positive electrode active material or a positive electrode active material prepared by the method for preparing the positive electrode active material, wherein the positive electrode active material has high ionic conductivity and electronic conductivity, and when the positive electrode sheet is applied to a lithium-ion battery, the battery can have high magnification performance.

[0008] This application provides a lithium-ion battery comprising the above-mentioned positive electrode active material or a positive electrode active material prepared by the above-mentioned method for preparing the positive electrode active material or the positive electrode sheet, wherein the lithium-ion battery has high magnification performance. [Means for solving the problem]

[0009] This application provides a positive electrode active material comprising secondary particles consisting of primary particles, wherein the primary particles have the chemical composition shown in Formula 1. Li 1+a Fe 1-x-y Mn x A y (PO4) Formula 1 In Equation 1, -0.1 ≤ a ≤ 0.4, 0.5 ≤ x ≤ 0.7, 0 ≤ y ≤ 0.01, and A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. The crystallinity of the positive electrode active material is 98% or higher.

[0010] Furthermore, the positive electrode active material further includes a carbon coating layer that covers the surface of the primary particles, The mass percentage content of carbon in the positive electrode active material is 1.8 to 2.0 wt%.

[0011] Furthermore, the specific surface area of the positive electrode active material is 17 to 22 m 2 / g, and / or the powder compression density of the positive electrode active material is 2.1 to 2.4 g / cm 3 .

[0012] Furthermore, the median particle size of the primary particles is 0.25 to 0.4 μm, and / or the median particle size of the secondary particles is 5 to 6 μm.

[0013] The present application further provides a method for preparing the positive electrode active material according to any one of the above items, and the preparation method includes Step (1) of adding a first raw material and deionized water to a second raw material to obtain a first mixed slurry, wherein the second raw material includes a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant, and the first raw material includes lithium iron manganese phosphate having a chemical composition shown in Formula 2 Li 1+b Fe 1-c Mn c PO4 Formula 2 In Formula 2, -0.1 ≤ b ≤ 0.4, 0.5 ≤ c ≤ 0.7, Step (1), and Step (2) of polishing the first mixed slurry to obtain a second mixed slurry, wherein the median particle size of the second mixed slurry is 200 to 400 nm, Step (2), and Step (3) of granulating the second mixed slurry to obtain a third raw material having a median particle size of 3 to 4 μm, and Step (4) of sintering the third raw material at a sintering temperature of 65 to 670 °C, a sintering time of 6 to 8 h, and a heating rate of 3 to 8 °C / min under a protective atmosphere to obtain the positive electrode active material.

[0014] Furthermore, in Step (1), the first raw material further includes lithium iron phosphate Li3Fe2(PO4)3 and lithium manganese phosphate LiMnPO4 The first raw material includes 75 to 84 wt% of lithium iron manganese phosphate, 7 to 10 wt% of lithium iron phosphate, and 9 to 15 wt% of lithium manganese phosphate in terms of mass percentage content And / or, the first raw material accounts for 10-15% of the theoretical mass of the cathode active material produced.

[0015] Furthermore, in step (1), the second raw material further contains a carbon source, the carbon source accounting for 8-12% of the total mass of the theoretically produced cathode active material and the first raw material.

[0016] Furthermore, in step (2), the polishing includes a first polishing and a second polishing, The polishing speed for the first polishing method described above is 1400-1700 r / min, and the polishing time is 50-70 min. The polishing speed for the second polishing method is 1600-2000 r / min, and the polishing time is 50-70 min.

[0017] The present invention further provides a positive electrode sheet comprising a positive electrode active material described in any one of the above paragraphs or a positive electrode active material prepared by a method for preparing a positive electrode active material described in any one of the above paragraphs.

[0018] The present invention further provides a lithium-ion battery comprising a positive electrode active material described in any one of the above paragraphs or a positive electrode active material prepared by a method for preparing a positive electrode active material described in any one of the above paragraphs or the positive electrode sheet described above. [Effects of the Invention]

[0019] The positive electrode active material in this application includes secondary particles composed of primary particles, the primary particles have the chemical composition of formula 1 and have a crystallinity of 98% or more, and have a low content of heterophase (Li3Fe2(PO4)3 and LiMnPO4), which effectively improves the ionic conductivity and electronic conductivity of the positive electrode active material and further effectively improves the magnification performance of the battery. [Brief explanation of the drawing]

[0020] [Figure 1] This is an SEM diagram of the cathode active material in Example 1 of the present application. [Figure 2]This is an XRD diagram of the first raw material in Example 1 of the present application. [Figure 3] These are XRD diagrams of the cathode active materials in Example 1 and Comparative Example 1 of this application. [Modes for carrying out the invention]

[0021] To further clarify the purpose, technical solutions, and advantages of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Of course, the embodiments described are not all embodiments, but only a selection of embodiments of the present application. All other embodiments obtained by a person skilled in the art without creative work based on the embodiments of the present application are all within the scope of protection of the present application.

[0022] A first aspect of the present application provides a positive electrode active material comprising secondary particles consisting of primary particles, the primary particles comprising the chemical composition shown in Formula 1, Li 1+a Fe 1-x-y Mn x A y (PO4) Formula 1 In Equation 1, -0.1 ≤ a ≤ 0.4, 0.5 ≤ x ≤ 0.7, 0 ≤ y ≤ 0.01, and A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. The crystallinity of the cathode active material is 98% or higher.

[0023] Specifically, the crystallinity of the cathode active material can be determined by obtaining the diffraction peak area A1 of the crystalline phase and the diffraction peak area A2 of the amorphous phase from the XRD pattern, and the crystallinity can be calculated using Equation 2. Crystallinity (%)=A1 / (A1+A2)×100% Formula 2 The positive electrode active material in this application contains secondary particles composed of primary particles, the primary particles having the chemical composition shown in Formula 1 and a crystallinity of 98% or higher. Because the positive electrode active material inevitably contains heterophases with low ionic and electronic conductivity, namely Li3Fe2(PO4)3 and LiMnPO4, it is difficult to intercept and release lithium ions contained in the heterophase during the charge-discharge process, reducing the battery's multiplier performance. However, because the crystallinity of the positive electrode active material in this application is 98% or higher, the heterophase content in the positive electrode active material is low, effectively improving the overall ionic and electronic conductivity of the positive electrode active material, thereby enabling the lithium-ion battery to have high multiplier performance.

[0024] Furthermore, since some lithium ions in the positive electrode active material are distributed in the heterophase, the presence of the heterophase reduces the number of lithium ions that can move freely, and therefore, the positive electrode active material of this application has an even higher capacity.

[0025] Specifically, the heterophase content in the cathode active material can be calculated by fitting the XRD measurement pattern to an XRD standard card.

[0026] In one specific embodiment, the positive electrode active material further includes a carbon coating layer covering the surface of the primary particles, and the mass percentage content of carbon in the positive electrode active material is 1.8 to 2.0 wt%. Specifically, the mass percentage content of carbon can be measured by a carbon-sulfur analyzer. By carbon coating the surface of the primary particles, the electronic conductivity can be further improved, thereby giving the battery higher multiplier performance. At the same time, the carbon coating layer can further reduce the contact area of ​​the positive electrode active material with the electrolyte, avoiding side reactions with the electrolyte and giving the battery good cycle performance. When the mass percentage content of carbon in the positive electrode active material is within the above range, not only can the electronic conductivity of the positive electrode active material be effectively increased, but the lithium ion transfer path is shortened, and the specific capacity and multiplier performance are increased without hindering the intercalation and release of lithium ions. Specifically, the mass percentage content of carbon here refers to the total mass percentage content of carbon contained in the positive electrode active material.

[0027] In one specific embodiment, the specific surface area of ​​the cathode active material is 17-22 m². 2 The value is / g. Within this range, the positive electrode active material has a high specific surface area, which increases the contact area between the electrode and the electrolyte to some extent, improving the electrochemical reaction rate and further enhancing the battery's multiplier performance. At the same time, its specific surface area is not too large, effectively reducing the occurrence of side reactions, lowering the initial irreversible lithium loss, and giving the battery good cycle performance.

[0028] In one specific embodiment, the compressed powder density of the cathode active material is 2.1 to 2.4 g / cm³. 3 Within this range, the positive electrode sheet has a high compressive density and does not hinder the movement of lithium ions, resulting in a battery with high multiplier performance and high energy density.

[0029] In one specific embodiment, the median particle size of the primary particles is 0.25 to 0.4 μm. When the median particle size of the primary particles is within this range, the lithium ion migration path is short, and the magnification performance of the cathode active material can be further improved.

[0030] In one specific embodiment, the median particle size of the secondary particles is 5-6 μm. Within this range, the particle size of the secondary particles is relatively appropriate, the lithium ion diffusion pathway is short, and the magnification performance of the lithium-ion battery containing the positive electrode active material is further improved.

[0031] A second aspect of this application provides a method for preparing a positive electrode active material according to any one of the above-mentioned items, the preparation method being: Step (1) is to add the first raw material and deionized water to the second raw material to obtain a first mixed slurry, wherein the second raw material comprises a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant, and the first raw material comprises lithium iron manganese phosphate having the chemical composition shown in formula 2. Li 1+b Fe 1-c Mn c PO4 formula 2 In equation 2, step (1) is given by -0.1 ≤ b ≤ 0.4 and 0.5 ≤ c ≤ 0.7, Step (2) involves polishing a first mixed slurry to obtain a second mixed slurry, wherein the median particle size of the second mixed slurry is 200-400 nm. Step (3) involves granulating the second mixed slurry to obtain a third raw material with a median particle size of 3-4 μm, The method includes step (4) of sintering a third raw material in a protective atmosphere at a sintering temperature of 650-670°C, a sintering time of 6-8 hours, and a heating rate of 3-8°C / min to obtain a cathode active material.

[0032] Specifically, in step (1), a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant are mixed to obtain a second raw material. The first raw material and deionized water are added to the second raw material, and the first raw material contains lithium iron manganese phosphate having the chemical composition shown in formula 2, to obtain a first mixed slurry. The solid-liquid ratio of the first mixed slurry is preferably 1:3 to 1:5.

[0033] In this application, "lithium source" refers to a raw material that provides the element lithium, "iron source" refers to a raw material that provides the element iron, "manganese source" refers to a raw material that provides the element manganese, "phosphorus source" refers to a raw material that provides the element phosphorus, and "dopant" refers to a compound containing at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. Any compound containing the target element (lithium, iron, manganese, phosphorus) falls within the limitations of this application, and one target element may be introduced into the reaction system via one or more raw materials. For example, the lithium source can be selected from at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium oxalate; the iron source can be selected from at least one of iron phosphate, diferric oxide, iron nitrate, and iron oxalate; the manganese source can be selected from at least one of manganese carbonate, trimanganese tetroxide, manganese nitrate, manganese chloride, and manganese sulfate; and the phosphorus source can be selected from at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, ammonium phosphate, and ammonium monohydrogen phosphate. It should be interpreted that if a raw material contains two or more elements simultaneously, the raw material can be understood as an elemental source for two target elements. For example, if the raw material is lithium dihydrogen phosphate, it functions as both a lithium source and a phosphorus source.

[0034] This application does not specifically limit the molar ratio of the lithium source, iron source, manganese source, phosphorus source, and dopant, as long as the chemical formula of the prepared cathode active material satisfies Equation 1.

[0035] This invention does not limit the specific sources of lithium, iron, manganese, phosphorus, and dopants, which can be obtained, for example, by commercially available or conventional manufacturing methods.

[0036] The present invention is not specifically limited to the mixing method, and examples include any one of the following mixing methods: mechanical stirring, liquid stirring, or gas stirring, provided that the second raw material and the first raw material are thoroughly mixed in deionized water.

[0037] In step (2), the first mixed slurry is polished to obtain the second mixed slurry, and since the median particle size of the second mixed slurry is 200-400 nm, the second and first raw materials contained in the second mixed slurry are fine and uniform with smooth surfaces, the first raw material is uniformly dispersed in the second mixed slurry, and in the subsequent sintering process, more uniform cathode active material particles are formed, which is advantageous for increasing the crystallinity of the cathode active material.

[0038] In step (3), the second mixed slurry after polishing is granulated and reformed, preferably by selecting a spray dryer to perform granulation reformation, and a third raw material is obtained with an inlet temperature of 200-210°C, an outlet temperature of 90-95°C, and a particle size of 3-4 μm.

[0039] In step (4), the third raw material is heated in a protective atmosphere, and the temperature is raised from room temperature to a sintering temperature of 650-670°C at a heating rate of 3-8°C / min, followed by heat-hold sintering for 6-8 hours to obtain the sintered product. During this process, the first raw material decomposes at high temperature, forming crystal nuclei, which induces the rapid growth of metal ions in the second raw material along the active crystal plane of the first raw material, effectively suppressing the formation of heterophases. The sintered product is then crushed and sieved through a sieve to obtain a cathode active material with high crystallinity.

[0040] This application does not specifically limit the protective atmosphere, but exemplary, the protective atmosphere may be selected from argon gas, nitrogen gas, or helium gas.

[0041] This application does not specifically limit the grinding method and sieve, but exemplifies grinding by jaw crusher / roll crusher, mechanical grinding, and airflow mill classification grinding, and the mesh count of the sieve is preferably 280 mesh.

[0042] The method for preparing the positive electrode active material in this application involves reacting lithium manganese phosphate and lithium iron phosphate contained in the first raw material with the second raw material to produce new lithium manganese iron phosphate. Simultaneously, the metal elements in the second raw material rapidly grow along the active crystal plane of lithium manganese iron phosphate in the first raw material. This effectively reduces the heterophase content in the positive electrode active material and improves its crystallinity, ensuring that the crystallinity falls within the specified range. At the same time, since the first raw material can be directly decomposed into crystal nuclei during the heating process, this preparation method accelerates the crystallization of the system, shortens the reaction time, reduces the reaction temperature, and achieves the objectives of cost reduction and efficiency improvement.

[0043] In one specific embodiment, in step (1), the first raw material further comprises lithium iron phosphate Li3Fe2(PO4)3 and lithium manganese phosphate LiMnPO4, The first raw material contains, by mass percentage, 75-84 wt% lithium manganese iron phosphate, 7-10 wt% lithium iron phosphate, and 9-15 wt% lithium manganese phosphate. When the amounts of lithium manganese iron phosphate, lithium iron phosphate, and lithium manganese phosphate contained in the first raw material are within the above ranges, the heterophase content in the final prepared cathode active material becomes lower, resulting in higher crystallinity, and furthermore, the lithium-ion battery has higher magnification performance.

[0044] In one specific embodiment, the first raw material accounts for 10-15% of the theoretically generated mass of the positive electrode active material. Within this range, its crystallinity is significantly improved, and the positive electrode active material is given high ionic conductivity and electronic conductivity, thereby improving the multiplier performance of the lithium-ion battery.

[0045] The method for calculating the theoretical mass of the positive electrode active material in this application is as follows: If the molar ratio of lithium source, iron source, manganese source, phosphorus source, and dopant in the first raw material is (1+a):(1-xy):x:1:y, then the theoretical mass of 1 mol of positive electrode active material can be calculated by equation 3. Theoretical mass produced (g) of 1 mol of positive electrode active material = (1+a)×M1+(1-xy)×M2+x×M3+M4+y×M5 Equation 3 In Equation 3, M1 is the molar mass of Li, M2 is the molar mass of Fe, M3 is the molar mass of Mn, and M4 is PO4 - This is the molar mass of A, and M5 is the molar mass of A.

[0046] In one specific embodiment, in step (1), the second raw material further contains a carbon source, which accounts for 8-12% of the total mass of the theoretically generated positive electrode active material and the first raw material. During the sintering process, the carbon source decomposes at high temperatures, forming a coating layer on the surface of the primary particles, improving the conductivity of the positive electrode active material while effectively suppressing excessive growth of the primary particles. Within this range, the ionic and electronic conductivity of the positive electrode active material can be effectively increased, while simultaneously giving the battery high specific capacity and multiplier performance without hindering the intercalation and release of lithium ions.

[0047] The carbon source in this application refers to a raw material that provides a carbon element, and any material containing the target element is included in the limitations of this application, and one target element may be introduced into the reaction system via one or more raw materials. For example, the carbon source can be selected from at least one of glucose, sucrose, starch, polyvinyl alcohol, polyethylene glycol, citric acid, and ascorbic acid.

[0048] In one specific embodiment, step (2) includes polishing a first polish and a second polish, The polishing speed for the first polishing step was 1400-1700 r / min, and the polishing time was 50-70 min. The polishing speed for the second polishing is 1600-2000 r / min, and the polishing time is 50-70 min. When the polishing speeds and polishing times for both the first and second polishing are within the above ranges, the first and second raw materials become finer and more uniform, and the first raw material is uniformly distributed by the second mixed slurry, further improving the uniformity and crystallinity of the cathode active material.

[0049] This invention is not specifically limited to the polishing methods of the first and second polishing processes. For example, the first polishing can be performed by selecting any of the basket mill, ball mill, or sand mill, and the second polishing can be performed by selecting either the sand mill or ball mill.

[0050] A third aspect of the present application provides a positive electrode sheet comprising a positive electrode active material prepared by the method for preparing the positive electrode active material of the first aspect or the positive electrode active material of the second aspect. Since the positive electrode active material has high crystallinity and also high ionic conductivity and electronic conductivity, applying a positive electrode sheet containing the positive electrode active material to a lithium-ion battery can effectively improve the battery's magnification performance.

[0051] A fourth aspect of the present application provides a lithium-ion battery comprising a positive electrode active material prepared by a method for preparing a positive electrode active material of the first aspect or a positive electrode active material of the second aspect, or a positive electrode sheet of the third aspect. Because the lithium-ion battery comprises a positive electrode sheet of the third aspect, the lithium-ion battery has high magnification performance.

[0052] The cathode active material of this application will be described in detail below through specific examples.

[0053] Example 1 (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical mass of cathode active material. 1.757 kg of sucrose was weighed out so that it accounted for 10% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium iron manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and heat-hold sintering is performed for a heat-hold sintering time of 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.93%.

[0054] Example 2 (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical mass of cathode active material. 1.406 kg of sucrose was weighed out so that it accounted for 8% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is coarsely ground at a grinding speed of 1700 r / min for 60 minutes, and then coarsely ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 3°C / min from room temperature to a sintering temperature of 670°C, and heat-hold sintering is performed for a heat-hold sintering time of 8 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.85%.

[0055] Example 3 (1) 2.39 kg of lithium hydroxide, 6.78 kg of manganese carbonate, 3.19 kg of ferric oxide, 11.50 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed and mixed in a molar ratio of 1:0.59:0.2:1:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg. 1.88 kg of the first raw material was weighed so that it accounted for 12% of the theoretical mass of cathode active material. 2.108 kg of sucrose was weighed out so that it accounted for 12% of the theoretical mass of the cathode active material and the total mass of the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 8°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.96%.

[0056] Example 4 (1) 5.10 kg of lithium oxalate, 6.78 kg of manganese carbonate, 5.75 kg of ferrous oxalate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material was weighed so that it accounted for 12% of the theoretical mass of cathode active material. Then, 1.757 kg of sucrose was weighed out so that it accounted for 10% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is coarsely ground at a grinding speed of 1700 r / min for 70 minutes, and then coarsely ground again at a grinding speed of 2000 r / min for 70 minutes to obtain a second mixed slurry with a median particle size of 200 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 8°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.92%.

[0057] Example 5 (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed out in molar ratios of 0.50:0.59:0.4:0.6:0.01 and mixed to obtain the second raw material. 100 mol The theoretical production mass of the positive electrode active material is 15.69 kg. 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical production mass of the positive electrode active material. 1.757 kg of sucrose is weighed out so that it accounts for 10% of the total mass of the theoretical production mass of the positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material are mixed, and deionized water is added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contains, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate is LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1400 r / min for 50 minutes, and then roughly ground at a grinding speed of 1600 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 400 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 3°C / min from room temperature to a sintering temperature of 670°C, and heat-hold sintering is performed for a heat-hold sintering time of 8 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.90%.

[0058] Example 6 (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of positive electrode active material is 15.69 kg. 1.88 kg of the first raw material was weighed so that it accounted for 12% of the theoretical mass of positive electrode active material. 1.757 kg of sucrose was weighed out so that it accounted for 10% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 75 wt% lithium iron manganese phosphate, 10 wt% lithium iron phosphate, and 15 wt% lithium iron manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1400 r / min for 50 minutes, and then roughly ground at a grinding speed of 1600 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 400 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 3°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.93%.

[0059] Example 7

[0060] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical mass of cathode active material. 1.757 kg of sucrose was weighed out so that it accounted for 10% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 84 wt% lithium iron manganese phosphate, 7 wt% lithium iron phosphate, and 9 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 70 minutes, and then roughly ground at a grinding speed of 2000 r / min for 70 minutes to obtain a second mixed slurry with a median particle size of 200 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 8°C / min from room temperature to a sintering temperature of 670°C, and then heat-hold sintering is performed for 8 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.90%.

[0061] Example 8

[0062] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg. 1.88 kg of the first raw material was weighed so that it accounted for 12% of the theoretical mass of cathode active material. The first and second raw materials were mixed, and deionized water was added to obtain the first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron phosphate is LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4)

[0063] Example 9

[0064] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of positive electrode active material is 15.69 kg. 1.88 kg of the first raw material was weighed so that it accounted for 12% of the theoretical mass of positive electrode active material. 2.460 kg of sucrose was weighed out so that it accounted for 14% of the theoretical mass of the cathode active material and the total mass of the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 2.11%.

[0065] Example 10

[0066] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical mass of cathode active material. 1.054 kg of sucrose was weighed out so that it accounted for 6% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.81%.

[0067] Example 11

[0068] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical mass of cathode active material. 0.703 kg of sucrose was weighed out so that it accounted for 4% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium iron manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.52%.

[0069] Example 12

[0070] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed in a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg, and 1.88 kg of the first raw material is weighed out so that it accounts for 12% of the theoretical mass of cathode active material. 1.757 kg of sucrose was weighed out so that it accounted for 10% of the total mass of the theoretically generated positive electrode active material and the first raw material. The first raw material, sucrose, and second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium iron manganese phosphate, and the chemical composition of lithium iron manganese phosphate was LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1400 r / min for 50 minutes, and then roughly ground at a grinding speed of 1200 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 510 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, with the inlet temperature of the spray dryer being 210°C and the outlet temperature being 95°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.92%.

[0071] Example 13

[0072] (1) 3.69 kg lithium carbonate, 6.78 kg manganese carbonate, 6.03 kg iron phosphate, 6.90 kg ammonium dihydrogen phosphate, 0.04 kg magnesium oxide Mole ratio The first raw material was weighed in the ratios 0.50:0.59:0.4:0.6:0.01 and mixed to obtain the second raw material. The theoretical mass of 100 mol of cathode active material is 15.69 kg. 1.88 kg of the first raw material was weighed so that it accounted for 12% of the theoretical mass of cathode active material. 1.757 kg of sucrose was weighed so that it accounted for 10% of the total mass of the cathode active material and the first raw material. The first raw material, sucrose, and the second raw material were mixed, and deionized water was added to obtain the first mixed slurry with a solid-liquid ratio of 1:4. The first raw material contained, by mass percentage, 80 wt% lithium iron manganese phosphate, 8 wt% lithium iron phosphate, and 12 wt% lithium manganese phosphate, and the chemical composition of lithium iron manganese phosphate is LiFe 0.4 Mn 0.6 This is PO4. (2) The first mixed slurry is roughly ground at a grinding speed of 1700 r / min for 60 minutes, and then roughly ground at a grinding speed of 1800 r / min for 50 minutes to obtain a second mixed slurry with a median particle size of 330 nM. (3) The second mixed slurry is granulated and reformed using a spray dryer to obtain a third raw material with a median particle size of 3.9 μm, with the inlet temperature of the spray dryer being 190°C and the outlet temperature being 85°C. (4) The third raw material is heated in a nitrogen gas protective atmosphere at a heating rate of 5°C / min from room temperature to a sintering temperature of 650°C, and then heat-hold sintering is performed for 6 hours to obtain the positive electrode active material of this embodiment, the chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 The material is (PO4), and a carbon coating layer is applied to the surface of the primary particles of the positive electrode active material. When measured by a carbon-sulfur analyzer, the mass percentage content of the elemental carbon in the positive electrode active material was found to be 1.94%.

[0073] Comparative Example 1 In this comparative example, the preparation method for the cathode active material is almost identical to that of Example 1, except that the first raw material is not added, and sucrose accounts for 10% of the theoretical mass of the cathode active material produced, amounting to 1.569 kg.

[0074] Comparative Example 2 In step (1), the preparation method for the cathode active material in this comparative example is almost identical to that of Example 1, except that the first raw material is not added, the sintering temperature is 700°C, and the sintering time is 12 hours.

[0075] Comparative Example 3 The preparation method for the cathode active material in this comparative example is almost identical to that in Example 1, except that magnesium oxide, which is a dopant, is not added in step (1).

[0076] Comparative Example 4 Except for the sintering temperature being 620°C, the sintering time being 5 hours, and the heating rate being 10°C / min during step (3), the method for preparing the cathode active material in this comparative example is almost identical to that of Example 1.

[0077] Comparative Example 5 In step (2), the preparation method for the cathode active material in this comparative example is almost identical to that of Example 1, except that the first mixed slurry is coarsely ground at a polishing speed of 1700 r / min for 70 minutes, and then coarsely ground at a polishing speed of 2200 r / min for 90 minutes to obtain a second mixed slurry with a median particle size of 165 nM.

[0078] Comparative Example 6 In step (3), the inlet temperature of the spray dryer is 230°C and the outlet temperature is 110°C, and a third raw material with a median particle size of 2.7 μm is obtained. Except for these differences, the method for preparing the cathode active material in this comparative example is almost identical to that in Example 1.

[0079] Test example 1. The physicochemical properties of the cathode active materials prepared in the above examples and comparative examples are characterized, and the characterization results are shown in Table 1. Then, as shown in Figure 1, SEM characterization is performed on the cathode active material prepared in Example 1.

[0080] Figure 1 is an SEM image of the positive electrode active material of Example 1. As can be seen from Figure 1, the positive electrode active material has high uniformity of primary particles, good sphericity of secondary particles, and the distance between positive electrode active material particles can be shortened. + This improves the transport speed and, by roughening the surface of the positive electrode active material, increases the contact area between the positive electrode active material and the electrolyte, thereby improving the reaction speed of the battery and resulting in a battery with high magnification performance.

[0081] 2. As shown in Figures 2 and 3, XRD characterization was performed on the first raw material of Example 1, the cathode active material of Example 1, and the cathode active material of Comparative Example 1.

[0082] Figure 2 is the XRD diagram of the first raw material in Example 1, and Figure 3 is the XRD diagram of the cathode active material in Example 1 and Comparative Example 1. As can be seen from Figure 2, the first raw material is manganese iron lithium LiFe phosphate. 0.4 Mn 0.6 The material contains PO4, lithium iron phosphate (Li3Fe2(PO4)3), and lithium manganese phosphate (LiMnPO4). This is because, during the preparation of the first raw material in an air environment, some of the lithium iron manganese phosphate decomposes, generating a heterophase (Li3Fe2(PO4)3 and LiMnPO4). As a result, the first raw material inevitably contains these two heterophases. As can be seen from Figure 3, the content of the heterophase in the cathode active material prepared after adding the first raw material is low, while the content of the heterophase in the cathode active material prepared without adding the first raw material is high. Thus, the cathode active material in Example 1 has a low heterophase content and high crystallinity.

[0083] 3. The cathode active materials prepared in the above examples and comparative examples are applied to lithium-ion batteries, and the specific steps are as follows. The cathode active material prepared as described above in a mass ratio of 80:10:10, the conductive agent carbon black, and the binder polyvinylidene fluoride are mixed and dispersed in N-methylpyrrolidone to form the cathode active material. FoodA rally is prepared, applied to the surface of an aluminum foil current collector, dried, rolled, slit, and tab-welded to obtain a positive electrode sheet, which is then combined with a PE / PP composite separator, a lithium sheet, and an electrolyte to prepare a CR2032 batane battery. The electrolyte contains 1 mol / L lithium hexafluoride phosphate and ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[0084] The prepared Batane battery is then tested for magnification performance and cycle performance. (1) Magnification performance test The prepared Batane battery was charged and discharged in the voltage range of 2.0-4.3V, at 25°C, and at a multiplier of 0.1C. It was then cycled three times at 0.33C and five times at 1C to obtain the charge and discharge conditions of the battery at different multipliers, and the results are shown in Table 2. (2) Cycle performance test At 25°C, the prepared Batane battery is charged and discharged 500 times at 2.0-4.3V and 1C. The initial discharge capacity is defined as C0, and the discharge capacity after 500 cycles is defined as C1. The capacity retention rate for 500 cycles is calculated using Equation 4. Capacity retention rate after 500 cycles (%) = (C1 / C0) × 100% Equation 4

[0085] The test results are shown in Table 2.

[0086] [Table 1]

[0087] [Table 2]

[0088] As can be seen from Table 1 and Table 2, The positive electrode active materials of Examples 1-13 have higher crystallinity, lower heterophase content, and higher ion diffusion coefficient and electronic conductivity compared to the positive electrode active materials of Comparative Examples 1-6. At the same time, the Batan battery containing the positive electrode active materials of Examples 1-13 has higher capacity retention and magnification performance. The crystallinity of the positive electrode active materials of Examples 1-13 can reach at most 99.6%, the heterophase content is at least 0.2%, and the ion diffusion coefficient is at most 7.9 × 10⁻⁶. -13 As such, the electronic conductivity is at most 2.62 S / m, the corresponding capacity retention rate is at most 96.2%, and the magnification performance is at most 98.6%. As can be seen from this, the positive electrode active material of the present invention has a higher crystallinity and can significantly improve the magnification performance of lithium-ion batteries.

[0089] Finally, it should be noted that the above embodiments are not limitations, but merely serve to illustrate the technical solutions of the present application. While the present application has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical means described in the above embodiments or substitute some of their technical features, and these modifications or substitutions should be understood not to cause the essence of the corresponding technical means to deviate from the spirit and scope of the technical means of the embodiments of the present application.

[0090] [Cross-reference of related applications] This application claims priority to the Chinese patent application filed with the China National Patent Office on December 14, 2023, with application number 202311729060.2 and title "Cathode Active Material and Method for Preparing the Same," all of which are incorporated herein by reference.

Claims

1. A positive electrode active material comprising secondary particles consisting of primary particles, wherein the primary particles have the chemical composition shown in Formula 1. Li １＋ａ Fe １－ｘ－ｙ Mn ｘ A ｙ (PO ４ ) Formula 1 In Equation 1, -0.1 ≤ a ≤ 0.4, 0.5 ≤ x ≤ 0.7, 0 ≤ y ≤ 0.01, and A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. The cathode active material having a crystallinity of 98% or more.

2. The positive electrode active material further comprises a carbon coating layer covering the surface of the primary particles, The positive electrode active material according to claim 1, wherein the mass percentage content of carbon element in the positive electrode active material is 1.8 to 2.0 wt%.

3. The specific surface area of ​​the aforementioned positive electrode active material is 17 to 22 m². ２ The powder compression density of the positive electrode active material is 2.1 to 2.4 g / cm³. ３ The positive electrode active material according to any one of claims 1 or 2.

4. The positive electrode active material according to any one of claims 1 to 3, wherein the median particle size of the primary particles is 0.25 to 0.4 μm, and / or the median particle size of the secondary particles is 5 to 6 μm.

5. A method for preparing a positive electrode active material according to any one of claims 1 to 4, Step (1) to obtain a first mixed slurry by adding a first raw material and deionized water to a second raw material, wherein the second raw material comprises a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant, and the first raw material comprises lithium iron manganese phosphate having the chemical composition shown in formula 2. Li １＋ｂ Fe １－ｃ Mn ｃ PO ４ Formula 2 In equation 2, step (1) is given by -0.1 ≤ b ≤ 0.4 and 0.5 ≤ c ≤ 0.7, Step (2) involves polishing the first mixed slurry to obtain a second mixed slurry, wherein the median particle size of the second mixed slurry is 200 to 400 nm. Step (3) involves granulating the second mixed slurry to obtain a third raw material having a median particle size of 3 to 4 μm, A method for preparing a positive electrode active material, comprising the step (4) of sintering the third raw material in a protective atmosphere at a sintering temperature of 650 to 670°C, a sintering time of 6 to 8 hours, and a heating rate of 3 to 8°C / min to obtain the positive electrode active material.

6. In step (1), the first raw material is lithium iron phosphate Li ３ Fe ２ (PO ４ ) ３ and Lithium manganese phosphate LiMnPO ４ It further includes, The first raw material contains, by mass percentage, 75-84 wt% lithium manganese iron phosphate, 7-10 wt% lithium iron phosphate, and 9-15 wt% lithium manganese phosphate. and / or, the method for preparing a cathode active material according to claim 5, wherein the first raw material accounts for 10 to 15% of the theoretical mass of the cathode active material produced.

7. The method for preparing a cathode active material according to claim 5 or 6, wherein in step (1), the second raw material further comprises a carbon source, the carbon source accounting for 8 to 12% of the total mass of the theoretically produced cathode active material and the first raw material.

8. In step (2), the polishing includes a first polishing and a second polishing. The polishing speed for the first polishing method is 1400 to 1700 r / min, and the polishing time is 50 to 70 min. The method for preparing a positive electrode active material according to any one of claims 5-7, wherein the polishing speed of the second polishing is 1600 to 2000 r / min and the polishing time is 50 to 70 min.

9. A positive electrode sheet comprising a positive electrode active material prepared by any one of claims 1 to 4 or a method for preparing a positive electrode active material prepared by any one of claims 5 to 8.

10. A lithium-ion battery comprising a positive electrode active material prepared by any one of claims 1-4 or a method for preparing a positive electrode active material prepared by any one of claims 5-8 or a positive electrode sheet prepared by claim 9.

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